The synthesis of full and semi interpenetrating networks (IPNs) based on poly(dimethylsiloxane) (PDMS)/polystyrene, PDMS/polybutadiene and PDMS/poly(glycerylpropoxytriacrylate)(a)) is described. PDMS was used as host polymer in most cases. PDMS networks were prepared with two prepolymers having different number-average molecular weights between junctions, ($) over bar M(c) = 15 . 10(3) and ($) over bar M(c) = 75 . 10(3). Physical properties of IPN samples such as stress-strain behaviour, swelling and glass transition temperature (T-g) were examined. IPNs of both PDMS/polystyrene and PDMS/poly(glycerylpropoxytriacrylate) exhibit superior mechanical and elastomeric properties with respect to pure PDMS network. Most of the IPN systems studied in this work display two T(g)s and indicate phase separation.